Download 5. Chemical Bonding and Modern Electronics

5. Chemical Bonding and Modern Electronics
An atom’s valence electrons are strongly affected by interaction with other atoms
within bonding distance. If the electronegativity difference between the two atoms is
large, the valence electron(s) from the low electronegativity element are transferred to the
high electronegativity element forming an ionic bond. Ionic substances commonly form
solids that are held together by the coulombic attraction of the oppositely charged ions. If
the electronegativity difference between the atoms is small, then the atoms form a
covalent material. Covalent substances are held together by the valence electrons forming
an electronic wave that envelopes the nuclei involved. Covalent bonds are localized
between the atoms involved the bond.
Semiconducting solids consist of a network of covalent bonds. Due to the extended
network, the electronic states form a band of states. A gap in energy exists between the
fully occupied band formed from the valence states, called the valence band, and the
empty band formed from the next higher energy states, called the conduction band. The
size of the energy gap depends on the strength of interaction between the atoms in the
solid: A strong interaction results in a large gap while a weaker interaction results in a
small gap.
After completing this chapter you should be able to:
 Indicate where the majority of the electron density is when atoms of two elements
interact (Exercises 1-4)
 Classify substances as metallic, ionic, covalent (Exercises 5-10)
 Generate Lewis dot structures of molecules (Exercises 11, 13-14)
 Generate a molecular orbital energy level diagram for diatomic molecules: Use
molecular orbital energy level diagrams to determine bond order and relative stability of
neutral molecules and ions (Exercises 12, 15-26)
 Generate band diagrams for solids, generate hybrid orbitals (Exercises 27-32)
 Connect size and band gap (Exercises 33-36)
 Predict the relative band gap for mixed valence semiconductors (Exercises 37-46)
 Indicate the composition of a p-type semiconductor, an n-type semiconductor:
Indicate the composition for a p-n junction and determine the forward bias direction
(Exercises 47-56)
 Connect resistivity and band diagram (Exercises 57-62)
 Generate a band diagram for an oxide semiconductor: Explain how oxide
semiconductors differ from nonoxide semiconductors (Exercises 63-64)